1. Field of the Invention
The present invention relates to a method for measuring displacement of settlement and uplift of the bed inside the ground promptly by making use of current magnetic effect and an apparatus thereof.
2. Prior Art
Due to compaction by landfilling sand in ocean reclaiming works, ground excavation in underground work and drainage of underground water, the bed in the ground is subjected to settlement or uplift, which is gradually propagated to the ground surface to lead to bad influences on the structures above the ground or collapse accidents of roads etc. Accordingly, instead of controlling the settlement and uplift of the ground bed above the ground surface, recently, various methods and systems are developed to detect early occurrence of settlement or uplift in the bed inside the ground to prevent bad effects on the ground surface. The methods and apparatuses for measuring the fluctuations of the ground by depth and layer quantitatively and precisely have been disclosed, for example, in the Japanese Laid-open Patent Sho. 59-195122 and the Japanese Laid-open Utility Model Sho. 63-193304.
FIG. 5 shows an example of measuring the fluctuations by depth and layer of the prior art. A vertical hole is drilled from the ground surface into the ground 26, and a protective tube 25 is inserted and placed to protect the hole wall. At an arbitrary depth of the protective tube 25, a sinking element 3 which is a magnetic generating element is buried into the ground by striking the tube side wall by using a driving device. Each sinking element 3 driven in the ground moves up and down along with the variation of the bed of the position. To measure the depth of the sinking element 3, a detecting probe 23 having a magnetic detecting means such as magnetic sensor is lowered into the protective tube 25 by using a cable 22. When the detecting probe 23 comes to the location of the sinking element 3, a voltage is generated in the magneto-electrical converting element and this voltage is transmitted to the measuring instrument 24 above the ground by way of the cable 22. By measuring the let-off length of the cable 22 when this voltage is generated, the depth of the detecting probe 23, that is, the sinking element 3, from the ground surface can be measured. By measuring periodically the depth of the sinking element in this way, the fluctuations of the burying position of the sinking element, that is, the variation of the bed can be measured.